A phenomenon spreading through geographic space, such as a language. Silvestre and Campoy (2002) Studia Anglica Posnaniensia 38, conclude that models may give adequate statistical explanations for the volume, distance, and direction of geographical diffusion flows, but they do not reveal causal factors. Comparato and Mitchell (2010) http://dx.doi.org/10.2139/ssrn.1670344 employ a social learning model to examine the role of geography in the diffusion of US Supreme Court precedent in State Supreme Courts, and find that both the ideological distance between State Supreme Courts and the geographic proximity of states influences the likelihood of adoption re: Miranda v. Arizona.